Toshiba GR200 Series Instruction Manual page 134

Offset characteristics in ZS
Some elements in ZS are used for the detection of faults in the reverse direction and these
elements can have an offset characteristic, which assures the detection of a close-up three-
phase fault. Offset characteristic
instructs to start the memory action at which the voltage drops to zero upon the occurrence of
a fault. That is, for dropping to zero voltage, the memory action services an important role for
deciding whether the fault is located in the forward or in the reverse direction based upon the
relay location. In the offset characteristic, its offset value is fixed at 1.5Ω for 5A rating
whereas it is fixed at 7.5Ω for 1A rating
offset characteristic of Z1S in the reverse direction; Figure 2.10-22 illustrates that the action
of the Quad characteristic is applied. Note that the offset characteristic in the reverse direction
is not provided in Z2S and Z3S.
Note: As a rule, Z1S, Z1XS, and Z5S are utilized for a close-up three-phase fault. For
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example, the Z1S element can be instructed to operate in the reverse direction; the
operation of the Z1S element should be covered the origin (i.e., voltage=0), as
shown in Figure 2.10-21. Owing to the memory action for the close-up fault, the
Z1S element is able to detect a fault even if the memory does not hold voltage data
(say, in the memory the voltage data is set to zero for the close-up three-phase
fault). The operation of the memory action has been available for the last three-
cycles at the occurrence of the close-up fault; the memory action has not been
available for the last four-cycles. The same memory action is also provided in the
Z1XS and the Z5S.
Note: Either 1A or 5A rating is fixed to operate on a transfer modules (VCT). For more
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information about the VCT, see Chapter
module for AC analog input
Z1S-R.Reach
Z1S-R.Angle
Figure 2.10-21 Z1S Mho element during close up fault (Offset action)
is provided in Z1S, Z1XS, and Z5S; the offset characteristic
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. Figure 2.10-21 exemplifies the action of the Mho
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Technical Description: Transformer
.
Static MHO characteristic
X
Z1S-Mho.Angle
R
Z1S-X.Reach
- 111 -
6F2S1914 (0.49)
Offset MHO characteristic
during close-up fault
GRL200 (Soft 033 & 037)
,
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